The present invention relates to an improved process of preparing a polychloroprene latex.
The polymerization of chloroprene in an alkaline aqueous emulsion in the presence of emulsifying agents is well known. Depending on the final use of the polychloroprene, various formulations have been proposed, i.e., use of dissolved sulfur or of a chain transfer agent, addition of a peptizing agent, etc., which make it possible to obtain different grades of polychloroprenes within a specified viscosity range. The main obstacle encountered by manufacturers resides in the difficulty in obtaining a viscosity whose value remains constant between the moment when the polymerization reaction is complete and the moment when the polymer is isolated from the latex. This period generally is between 10 and 100 hours. In general, the viscosity has a tendency to increase during storage. This phenomenon, which is due to a slower or faster cross-linking depending on the operating conditions, is known as the aging of the latex. The increase in the viscosity during storage may or may not be accompanied by the appearance of a gel, resulting in a partial insolubilizing of the polychloroprene in preparations for adhesives and a substantial modification of the physical and rheological properties of the polymers.
In order to overcome this aging phenomenon, it has already been proposed to polymerize the chloroprene in the presence of specific carboxylic acid amides (French Patent application No. 76.20292, and corresponding U.S. Pat. No. 4,101,481.) These amides, which are very effective in protecting the polychloroprene against aging, have, however, a drawback upon their use industrially over long periods of manufacture. As a matter of fact, a progressive, abnormally high fouling of the equipment employed to prepare the modified latices using these carboxylic acid amides is noted.
It is, accordingly, an object of the present invention to provide a process for producing polychloroprene latices which are stable during aging and storage and which do not foul the equipment employed in the process.
It is another object of the invention to provide a process for preparing a polychloroprene latex employing a sulfonamide in the aqueous emulsion used to produce the latex.
Further objects of the invention comprise the improved polychloroprene latices of the invention and adhesive mixtures containing them.
Other objects will be apparent to those skilled in the art from the present description.